01 -
Drain the tuna well and flake into a bowl. Stir in mayonnaise, celery, mustard, lemon juice and pepper.
02 -
Butter one side of each bread slice thinly and evenly. Place two slices butter-side down on a board.
03 -
Divide half the cheddar between those slices. Add the tuna mixture, spreading it nearly to the edges, then top with the remaining cheddar.
04 -
Close with the other two bread slices, butter-side up. Heat a large skillet over medium-low heat.
05 -
Cook sandwiches for 4–5 minutes per side, pressing gently with a spatula, until the bread is golden and the cheese melts. Cover the pan briefly if the filling needs more time, lowering the heat so the bread does not burn.
06 -
Cut each sandwich diagonally and serve warm. If preparing for later, keep filling and bread separate until ready to cook for the crispest result.
07 -
Refrigerate unused tuna filling within two hours in a sealed container for up to three days. Cooked sandwiches are best fresh; refrigerate promptly and reheat thoroughly in a skillet.